GS 450h PCS warning light on

[Peter James Moore]

GS 450h PCS warning light on.

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Any suggestions/comments on the following would be appreciated. I recently bought a 2008 GS 450h Sports model with 54,000 miles. This is a new Japanese import. UK registration complete. Speedo converted to MPH and replacement English centre console fitted. Car drives perfectly but it does have two faults. One, the tyre pressure warning light is permanently on although the tyres are new and correctly inflated. Two - and I think this is more important, the PCS light together with a red warning triangle comes on whenever I reach 43 MPH. These lights stay on until I switch off the engine when, presumably the system re-sets. I can drive indefinitely below 43 MPH and the lights don't come on. The diagnostic machine at the garage I have used for decades read all the systems on the car but did not show any fault codes except the tyre pressure sensor. Here's a couple more odd features of the car that may or may not be related to the PCS problem. Driving away after starting the car does not lock the doors until the car is traveling at about 25 MPH. With all my previous cars with this feature the doors locked at around 5 - 7 MPH. On one occasion last week I had to brake a little harder than normal but this was not an emergency and there was zero chance of an accident but to my surprise the seat belt tensioners operated.. On another occasion I accidentally turned on either the parking sensors or the lane guide. The approach to my house is a narrow lane with a sharp corner edged with a wall. I might have expected a warning sound but not the loud warning buzzer and a flashing message to brake as the car passed the wall.. I have no idea what is causing the PCS fault light or why the diagnostic machine doesn't find the fault. I wondered if there is a faulty speed sensor relaying wrong information and the mechanic at my garage suggested that the device fitted to alter the speedo from km to MPH is faulty or fitted incorrectly.. Any suggestions please. I read a thread recently where somebody with a similar fault was encouraged to spend several thousands by his Lexus dealer on new PCS parts that might or might not fix the problem. I have no intention of going down that route but I would like to fix this on what is otherwise a truly awesome car.

[ColinBarber]

Your speedo conversion hasn't been implemented correctly and is affecting the speed signal that many of the vehicles systems are using. For PCS it receives a speed signal directly from the ABS/Skid control ECU and the combination meter and if the two go out of sync too much you will get a warning - it should produce an error code, maybe your system cannot read all proprietary error codes?

Doors automatically lock around 12 to 15 mph, so with a 1.6x speedo conversion that is affecting other systems that would equate to approx. 20 to 25 mph.

There are potentially other systems that will be affected by this incorrect speed signal so you will want to get this resolved.

[Sami Tilander]

About the TPMS warning: are you getting also message "Check System"? If yes, then the car's ECU cannot communicate with the TPMS sensors (one or more) of the wheels. You mentioned about new tyres: did you also got new sensors? Were they properly registered to the ECU?

BR.Sami

[Steven Lockey]

Oh yeah, sounds like a botched conversion job.

Makes a lot of sense you get messages over a certain speed given the way the hybrid works, it uses the speed of the car to some degree to work out what it needs to do.
Really should use shaft-speed but god knows how the programs are configured inside. A common issue in programming is devs not using the same source of truth.

It may be something like the computer is detecting the shocks should have stiffened but haven't because the shock controller thinks its getting km/h but its getting mph.

Plugging tech-stream in might give you a bit of a clue, maybe as simple as a setting that needs flipping that got forgotten. But at worst you can check the performance numbers
(not while driving) and see if it looks like there is a mismatch in the system somewhere.

[Peter James Moore]

Thank you all for your very useful thoughts and suggestions. Clearly this car is a complex piece of kit and there is no obvious answer. After further discussion with my mechanic we are considering taking out whatever adapter has been fitted and return the car to its factory settings. We have found a company here in the UK who  copies - exactly it seems - the original speedo dial and makes one that will show the MPH equivalent speed. This  way the car's ECU's will read km per hour and act accordingly but I will see MPH.  Any comments? Either way I'll post what happens if we try it If it doesn't work we will look again at the suggestions here.